Control circuit



Jy 3g 1945 J. R., MAHGNEY 5T AL CONTROL CIRCUIT Filed Aug. 19, l1944 2 SheeiS-She- 2 WTNESSES: '2' HNVENTQRS Patented July 30, 1946 CONTROL CIRCUIT John R. Mahoney, Pittsburgh, and Harry J. Bichsel, Forest Hills, Pa., assgnors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 19, 1944, Serial No. 550,231

(Cl. 32o-1) 7 claims. l

This invention relates to an electronic control circuit and has particular relation to a control circuit for use with a capacitor discharge Welder.

In an energy storage Welder of the capacitor discharge type, a bank of capacitors is charged from an alternating current supply source through a rectifier and is thereafter discharged through the primary winding of a welding transformer, the secondary Winding of which is connected across a pair of Welding electrodes in engagement with the material to be welded. It has been common practice to control the discharge of the capacitor bank by means of an electric discharge valve of the arc-like type, such as an ignitron, connected in series With the primary Winding of the welding transformer and the bank of capacitors. The series connected valve is rendered conductive by a timing circuit after the capacitor bank is charged to the desired voltage.

When the series connected valve becomes conductive, the capacitor bank is discharged through the primary winding of the welding transformer to effect a Weld.

As the discharge of the capacitor bank is completed, the energy stored in the magnetic core of the transformer and the secondary circuit during the discharge is released and tends to charge ycapacitor bankinversely. Such an arrangement is shown, for example, in the copending application of Clyde E. Smith and Clarence B. Stadum,

Serial No. 475,662, filed February 12, 1943.

. In many applications of capacitor discharge Welders, high speed operation is extremely desirable. For example, when a series of welds are to be made in rapid succession, correspondingly rapid charging and discharging of the capacitor bank is required. The rectifier employed to charge the capacitors in the bank is ordinarily arranged to supply charging current whenever vthe capacitor voltage is below a predetermined 'desired value. L thesame time that the series connectedvalve is lconductive, the current supplied through the rec- If the rectifier is in operation at tifer for charging the capacitor, would instead be passed through the series connected valve preventing the latter from becoming non-conductive to enable a new weld to be made. It is therefore necessary to block the operation of the rectier during the time that the series connected valve is conductive.

In the past, operation of the rectier during discharge of the capacitor bank has been prevented by means of an auxiliary timing circuit which was connected to the rectifier circuit and became effective at the time the series connected valve wasI rendered conductive.l The blocking time provided depended upon the voltage to which the capacitor bank had been charged. This arrangement is also shown in the aforementioned copending application of Smith and Stadum.

An auxiliary timing circuit as described to block the operation of the rectifier during the capacitor discharge operation is effective for that purpose. However, the actual length of the discharge time varies considerably for different transformers and different numbers and sizes of capacitors employed. In actual practice, the number of capacitors employed in the capacitor bank may be changed at will for different jobs. In addition, the control circuits may be applied to different welding transformers. Since the overall blocking time is substantially constant in the prior circuits for any capacitor voltage employed, the timing circuit must be arranged to give a blocking time of sufficient duration to take care of the longest discharge time. Such an arrangement obviously increases the overall time required for a welding operation in most cases and prevents the high speed successive Welding operations desired.

It is accordingly an object of our invention to provide a new and improved control circuit for a capacitor discharge Welder.

Another object of our invention is to provide a new and improved circuit for preventing charging of the capacitor bank during the normal discharge thereof in a capacitor discharge Welder.

A further object of our invention is to provide a novel control circuit for a capacitor discharge Welder in which' the speed of operation is considerably increased.

In accordance with our invention the operation of the charging rectifier is prevented only in response to actual current flow through the vvalve means controlling the fiow of current between the `primary Winding of the welding transformer and the capacitor bank. Thus, in a, Welder in which a series connected and a shunt connected valve Zi are used as described, the rectifier is blocked only as long as the series connected valve is conductive. As soon as the series connected valve becomes nonconductive, recharging of the capacitor is initiated although current may still be flowing in the circuit through the primary winding of the welding transformer and the shunt connected valve. As a result the speed of operation of the welder may be greatly increased.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to the organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: Y

Figure 1 is a schematic diagram illustrating our invention as embodied in a capacitor discharge Welder; and

Fig. 2 is a schematic diagram illustrating our invention as embodied in a capacitor discharge Welder of a different type.

As shown in Fig. 1 a variable capacitor 3 is connected to be charged from a source of alternating current through a rectifier charging circuit 'l and to be discharged through the primary winding 9 of a welding transformer i i. The secondary winding i3 of the transformer il is connected across a pair of welding electrodes i5 and l'l which are adapted to be moved relative'to each other to clamp the material i9 to be welded therebetween.

The charging circuit 'l receives its energy from the source 5 through a circuit breaker 2| and an auxiliary transformer 23. The charging circuit includes a pair of rectifier valves and 2l of the arc-like type, preferably thyratrons, having their anodes 29 and 3|, respectively connected to opposite end terminals 33 and 35 of the secondary winding 3l of the auxiliary transformer 23. The cathodes 38 and 39 of the valves 25 and 2l, respectively, are connected to each other and to one plate il of the capacitor 5. The other l plate |33 of the capacitor 3 is connected to a center tap of the secondary winding 3l. The grids 41 and t5, respectively, of the valves 25 and 2i are connected together through their respective grid resistors 5I and tween the grid resistors 5i and 53 is connected through another resistor to the cathodes 3l and 39 of the valves 25 and 2l. Consequently, the grids bil' and "i9 are normally at the same potential as the corresponding cathodes 38 and 3a. As a result, the charging circuit 7| constantly tends to supply direct current through the capacitor 3 to charge it to a predetermined value of voltage with the one plate il positive whenever the capacitor voltage is below the predetermined value. The value of the voltage is predetermined by the magnitude of the source voltage, the adjustment of the capacitor and the other circuit constants.

The positive plate il of the capacitor 3 is connected to one terminal 5l of the primary winding 9 of the welding transformer il with the other terminal 53 being connected to the other plate i3 of the capacitor tl through a small resistor Si and the anode 63 and cathode 55 of an electric discharge valve 6l of the arc-like type, such as an ignitron. Consequently, when the valve B'I becomes conductive, the capacitor 3 is discharged through the circuit including the primary winding 9, the resistor 5l and the Valve 5l.

The junction point be- An electric discharge valve 69 of the arc-like type such as a thyratron has its anode Il connected to the anode 53 of the valve 6l. and its cathode 'I3 connected to the ignition electrode 'I5 of the valve 5l. Valve 69 is hereinafter designated as a firing valve. When the firing valve 59 is rendered conductive, current starts to flow in the circuit extending from the capacitor 3 through the primary winding 9, the resistor 6|, the firing valve 69 and the ignition electrode I5 and cathode of the valve 61 to the capacitor 3.

This current renders the valve 61 conductive and the main discharge of the capacitor 3 is effected.

The control circuit of the firing valve 69 may be traced from the cathode 'I3 through a source of biasing potential such as a battery the secondary winding I9 of a peaking transformer 6I and a grid resistor 83 to the grid 85 of the firing valve 69. The biasing potential supplied from the battery 'Il normally maintains the firing valve 69 non-conductive to prevent discharge of the capacitor 3. However, a potential may be applied in the control circuit of the firing valve 69 through the peaking transformer 8| in a manner described hereinafter to render the firing valve 69 conductive.

When the capacitor 3 is discharged, the current flowing through the inductive primary winding 9 stores energy in the core of the welding transformer li as well as in the secondary winding circuit. As the discharge of the capacitor 3 is completed, the energy so stored is released tending to maintain the flow of current through the valve 51 to charge the capacitor 3 inversely with the plate 4| negative and the other plate t3 positive. To prevent this inverse charging, a second electric discharge valve 87 cf the arc-like type, preferably an ignitron, is connected in shunt across the primary winding 9 and in parallelwith the resistor SI, series connected valve 6'! and capacitor 3. The anode 89 of the shunt connected valve 8l is, of course, connected to the same ter.- minal 59 of the primary winding 9 as is the anode 63 of the series connected valve 61..

The firing circuit of the shunt connected valve @l may be traced from the cathode 9| through a second capacitor S3, the anode and cathode 9i' of anotherelectric discharge valve 99 (designated as a firing valve and preferably a thyratron) and a resistor IUI to the ignition electrode V23 of the shunt connected valve 8l. The'capacitor 9S is charged from the alternating current source through another auxiliary transformer |55, a rectier |01 and a resistor |09. Consequently, when the second firing valve 99 is rensuch as a battery H3 and a grid resistor I I5 to the grid I I'I of the valve 99. The biasing potential normally maintains iring valve 99 non-conductive. Another rectiner valve I I9 has its anode l2! connected to the anode 89 of the shunt 'valve 8| and its cathode |23 connected to the junction point between resisto-r III and battery II3,` When the energy stored in the Welding transformer and the secondary winding circuit is released, the polarity across the primary winding 9l changes and rectifier valve H9 becomes conductive. The

currentthen flowing through rectifier valve ||9 and resistor develops a potential across resistor to render firing valve 99 conductive to elect ring of the shunt connected valve 81. When the shunt connected valve 81 becomes conductive, the current flowing as a result of the release of energy at the primary winding 9 is conducted through the shunt valve. The series connected valve 61 becomes non-conductive at this time as the anode-cathode voltage thereof drops below the value necessary to maintain the arc therein.

Another auxiliary transformer |25 has its primary Winding |21 connected across the small resistor 6| which is in circuit between the primary wlnding 9 and the series connected valve 61.' The secondary winding |29 of the transformer |25 is connected across a resistor |3| which in turn is connected across another resistor |33 and a gas discharge tube such as a neon lamp |35.- For reasons which will be set forth hereinafter, the transformer |25 is one having sui'licient iron in its core and a sunicient number of turns so that it will not become substantially saturated under the conditions in which it is to be used, and will have a secondary winding output voltage of substantially the same Wave form as the voltage impressed across its primary winding.

Direct current voltage is supplied across a voltage divider |31 from the alternating current source through a transformer |39, a full Wave rectifier |4| and iiltering capacitors |43. The positive terminal |45 of the divider |31 is connected through the resistor 55 in the grid to cathode circuit of the valves 25 and 21 in the charging circuit 1, to the anode v|41 of an ampliiier tube such as a pentode |49, an RCA 6-C-6 tube being satisfactory. The cathode of th pentode |49 is connected to an intermediate point |53 of the divider |31, the negative terminal |55 of which is connected through the neon lamp |35 and a grid resistor |51 to the control grid |59 of the Apentodel Thus, the magnitude of the current flowing through the pentode |49, and consequently through the resistor 55 in series there- With, depends upon the voltage across the neon lamp |35. When the voltage supplied from the auxiliary transformer |25 is low, the pentode |49 is substantially non-conductive and no voltage is developed across the resistor 55 by current flowing through the pentode circuit. When the voltage supplied from the transformer |25 is high, the pentode |49 is conductive and the current flowing therethrough develops a potential across the resistor 55 of such magnitude and polarity as to prevent the valves 25 and 21 in the charging circuit 1 from becoming conductive. In other words, when the pentode |49 is conductive, the charging circuit 1 is prevented from operating.

The neonv lamp |35 serves to limit the maximum positive voltage on the grid l|59 of the pentode |49 without disturbing the wave form of the voltage supplied from the secondary winding |29 of the transformer |25 during the very iirst and very last parts of the discharge of capacitor 3. It is only by having the Wave form of the voltage developed across the secondary winding substantially the same as the wave form impressed across the primary winding that it is possible to eiect removal of the blocking potential from the charging circuit at the proper time. I

yIn operating the Welder illustrated in Fig.` 1, the circuit breaker 2| is iirst closed. The capac-4 itor 3 is then charged through the rectifier valves 25 and 21 until it. reaches a predetermined maximum voltage. A hand switch |6| may then be closed completing a circuit from one terminal of the source through the coil |63 of a solenoid valve |55, the hand switch |6| and a commutator |61 to the other terminal of the source. The commutator |61 is provided with conductive and non-conductive sections arranged to effect an opening and a closing of the circuit at timed intervals for a predetermined period of time. The commutator may be driven by `a synchronous motor |69 which is energized from the source. It is to be noted that the commutator |61 is merely illustrative of a repetitive timer and other timing means may be employed in place of the commutator. In actual practice electronic circuits such as is disclosed in the copending application of Pearson and Faulk, Serial No. 442,939, liled May 14, 1942, now Patent No. 2,354,140 dated July 18, 1944, are often used for this purpose.

When the commutator |61 completes the circuit through the coil |63 of the solenoid valve |65, the lower valve member |68 is closed and the upper valve member |1| is opened, completing a hydraulic circuit from an inlet pipe |13 to an outlet pipe |15. The outlet pipe |15 leads to a cylinder |11 containing a spring biased piston |19 to which one 0f the electrodes |5 is secured. Hydraulic pressure forces thispiston |19 downward until the electrodes |5 and |1 engage the material I9 to be welded, Thereafter, the back pressure in the hydraulic system operates through another pipe |8| to move another spring biased piston |83 to the left as illustrated in the drawings. Movement of the second piston |83 to the left closes a contactor |85 to complete a circuitl from a capacitor |81 through the contactor |85 and the primary winding |89 of the peaking transformer 8l, the secondary winding 19 of which is in the control circuit of the iirst firing valve 69. The capacitor |81 has been previously charged from a source of direct current potential such as a battery |9I, connected thereacross. Thus, when the contactor |85 completes the circuit, the capacitor |81 discharges through the peaking transformer 8| which impresses a potential in the first firing valve control circuit sufficient to render that valve conductive and fire the series connected Valve 61.

When the series connected valve 61 becomes conductive, the main capacitor 3 is discharged through the primary winding 9, the small resistorl 6| and the series connected valve 61 to effect a weld. Current iiowing through the resistor 6| acts through the auxiliary transformer |25 to lmpress a potential in the control circuit of the. pentode |49 causing the latter to become conductive. So long as the pentode |49`remains conductive, current flowing through the resistor 55 in circuit therewith develops a potential across the resistor 55 which prevents the valves 25 and 21 inthe charging circuit of the capacitor 3 from conducting any current to the capacitor 3 or to the discharge circuit therefor.

" It-is to be noted that the only current through the resistor 6| isthatwhich 'passes through the" T form as the voltage across the primary winding. Such a transformer insures the impressing in the input circuit of the pentode |419 of a potential to maintain the pentode conductive substantially until the series connected valve 61 becomes nonconductive.

As the initial discharge of the capacitor 3 through the primary winding 9 of the Welding transformer is completed, the stored energy is released tending to maintain the flow of current-through the series connected valve 61 to charge the capacitor 3 inversely. However, at that time the rectifier valve I9 becomes conductive causing the second firing valve 99 to render the shunt connected valve 81 conductive. The shunt connected valve 81 then conducts the entire current resulting from the release of stored energy so that the series connected valve 61 becomes 'non-conductive. At that instant the pentode |49 also becomes non-conductive and recharging of the capacitor 3 is initiated.

After the capacitor 3 is discharged, the commutator l 61 opens the circuit through the coil |63 of the solenoid valve |65 `permitting the piston |83 to be moved to open the contactor |85 in the ring circuit of the first firing valve 69 and permitting the electrode I5 to be moved out of engagement with the work i9 so that the work may be repositioned for a new weld. After a time interval suiiicient foi` the capacitor 3 to be recharged the commutator |61 again completes the circuit through the operating coil |23 of the solenoid valve 55 and another weld is initiated.

In Fig. 2 is illustrated a similar blocking circuit as applied to a different kind of capacitor dis- 1,

charge welder. This Welder is known as the full cycle welder and is disclosed and claimed in the copending application of Ezra T. Hughes and Stephen vL. Burgwin, Serial No. 511,575, filed November 2li, 1943. Here, the capacitor 3 is again charged from an alternating current source 5 through the same kind of a charging circuit 1 as was described in connection with Fig. 1 and the same reference characters are employed to designate corresponding elements.

The positive `plate 4| of the capacitor 3 is connected through the small resistor 6| to one side 59 of the primary winding 9 of the welding transformer Il. The other side 51 of the primary winding e is connected to the other plate t3 of the capacitor 3 through a pair of inversely connected valves 20| and 253, preferably ignitrons. The cathode 205 of the first valve 29| is connected to the negative plate 43 of the capacitor 3 and the anode 291 is connected to the positive plate il through the primary winding 9 and resistor 5|.

An electric discharge valve 299 of the arc-like type,v preferably a thyratron, which is hereinafter designated as a firing valve, is connected in series with a current limiting resistor 2| between the anode 291 and ignition electrode 2|3 of the first valve 29|. When the firing valve 209 is rendered conductive, current starts to iiow in the circuit extending from the positive `plate 4| of the capacitor 3 through the resistor 6|, the primary winding 9, the current limiting resistor 2| the firing valve 299, the ignition electrode 2| 3 and cathode 295 of the first valve 29| to the other plate 43 of the capacitor. This ignition current renders the first valve 29| conductive and the main discharge of the capacitor 3 through the primary winding 9 and the first valve 29| is effected.

The control circuit of the firing valve 299 may be traced from its cathode 215 through a source of biasing potential such as a battery 2 |1, the secondary winding 2|9 of a peaking transformer 22| and a grid resistor 223 to the grid 225 of the firing valve. The b-iasing potential supplied from the battery 211 normally maintains the firing valve 299 non-conductive to prevent discharge of the capacitor 3, However, a potential may be impressed in the control circuitI of the firing valve through the peaking transformer 22| in a manner described hereinafter to render the firing valve conductive, resulting in a discharge of the capacitor 3 through the primary winding 9 and valve 29|.

As vpreviously mentioned, the capacitor 3 is originally charged with one plate 4| positive and the other plate 43 negative. When the capacitor 3 is discharged, the discharge current flowing through the primary winding 9 stores energy in the welding transformer and the secondary circuit. As the discharge of the capacitor is completed, the energy so stored is released causing the capacitor to be charged inversely with plate 43 positive and plate 4I negative. The anode 221 of the second valve 293 is connected to the plate 49 while its cathode 2.29 is connected through the primary winding 9 and resistor 6| to the plate 4|. Consequently, if the second valve 293 is then rendered conductive, the inverse charge on the capacitor 3 is discharged through the valve 293, the primary winding 9 and resistor 6|.

Another electric discharge valve 23| of the arc-like type, preferably a thyratron, and also designated as a firing valve, is connected in series with a current limiting resistor 233 between the anode 221 and the ignition electrode 235 of the second valve 203. The grid 231 of firing valve 23| is connected through a grid resistor 239 to the cathode 24| of the firing valve. Consequently, when the resultant potential in the circuit consisting of the capacitor 3, the primary winding 9, resistor 5| and the valves 29| and 293, has the opposite polarity from the original charge on the capacitor, the firing valve 23| becomes conductive to render the second valve 293 conductive.

An auxiliary transformer |25 is also provided with its primary winding |21 connected across the small resistor 6| in the discharge circuit of the capacitor 3 and its secondary winding |29 connected to supply a control voltage for the pentode amplier tube |119, the output circuit of which is arranged to develop a potential across the resistor 55 to prevent operation of the charging circuit 1 while the pentode |119 is conductive. This blocking circuit is similar to the one described in connection with Fig. 1 but in addition a full wave rectifier 2133 is interposed between the secondary winding |29 of the auxiliary transformer |25 and the resistor ll. This full wave rectifier 243 is necessary in this circuit because current ows through the resistor 6| in both directions during the discharging operations of the capacitor 3. Another capacitor 245 is also connected across the resistor 55 in the output circuit of the pentode |29 to prevent too rapid a response to a decrease in potential across the resistor 5 l. In this way the momentary decrease in voltage across the resistor 6| as the current therethrough passes through zero during the discharging operation does not affect the blocking of the charging circuit 1.

A flux resetting circuit 241 is provided for reasons set forth in the aforesaid Hughes and Burgwin application. This circuit effects a flow T9. of direct current through a portion'l of the primary winding 9 as long as contactor 249 is closed. Contactor 249 is operated by pressure responsive 'piston |83 and is open during Welding operations and closed between successive operations.

When the circuit breaker 2| in Fig. 2 is first closed, the capacitor 3 is charged in the usual manner to the preselected voltage. To initiate a Welding operation the hand switch |6| is then closed `causing the hydraulic system to move electrodes I and l1 into engagement with the material I9 when commutator |61 completes the circuit. The hydraulic system moves piston |83 to the left, opening contactor 249 to open the flux resetting circuit 241 and closing a second contactor 25| to complete al circuit from the source through the coil 253 of a relay 255. The contactor 251 on the relay 255 in its deenergized position completes a charging circuit for an auX- iliary capacitor 259 from a direct current source 26|. When the relay 255 is energized, the charging circuit is opened and the contactor 251 closes a discharge circuit for the capacitor 259 through the primarywinding 253 of the peaking transformer 22|, the secondary winding of which is in the control circuit of the first firing valve 209. As a result the first valve is rendered conductive and the main capacitor 3 is discharged through the primary winding 9 of the weldin transformer The capacitor 3 thereafter re-v ceives an inverse charge before the current through the first valve 20| drops to zero. At that time the second valve 203 is rendered conductive and the inverse charge on the capacitor 3 is discharged back through the primary winding 9. During the period of conductivity of the first and second valves 20| and 203, current is owing through the resistor 6I in series therewith which acts through the auxiliary transformer and the pentode |49 to prevent operation of the charging circuit 'I for the main capacitor 3,. As soon as the second valve 203 becomes non-conductive the blocking potential on the charging circuit 'l is removed and recharging of the capacitor 3 by the charging circuit is initiated.

It is to be noted that while the initial discharge of the capacitor 3 through the first valve 20| is sufficient to produce a weld, the subsequent discharge of the inverse charge on the capacitor is not sufficient to eiect welding. The discharge of the inverse charge on the capacitor does, however, act to return the uX of the welding transformer a considerable way toward its original state. enabling the welding electrodes to be opened immediately thereafter without danger of arcing at the tips of the electrodes. Moreover, the portion of the inverse charge which is not employed in resetting the flux is again stored in the capacitor with the originalpolarity so that it is not wasted. The many advantages of such full cycle operation is fully set forth in the aforementioned copendlng application of Hughes and Burgwin.

Following the discharging operation the commutator |61 opens the circuit through the solenoid valve |65 causing the electrodes I5 and l1 to be opened, the flux resetting circuit to be reclosed and the relay 255 to be deenergized. After a time period during which the capacitors 3 and 259 are recharged, the commutator again completes the circuit through the solenoid valve and another welding operation is initiated.

Although we have shown and described a speciflc embodiment of our invention, we are aware that modifications thereof may be made without 1'0 departure from the inventive concepthere disclosed. We do not intend, therefore, to limit our invention to the specific embodiments described and illustrated.

We claim as our invention:

1. Apparatus for use in supplying current to a load comprising a capacitor, charging means connected across said capacitor and tending to supplycurrent therethrough to charge the same whenever the capacitor voltage is below a predetermined value, circuit means connecting said capacitor across said load to eiiect discharge ofsaid capacitor therethrough, said circuit means including valve means interposed between said capacitor and load for controlling the fiow of current therebetween and impedance means in series with said valve means whereby a voltage is developed across said impedance means in response to current conducted through said valve means, means responsive to said voltage and connected to said charging means for preventing operation of said charging means only during current'flow through said valve means, and control means connected to said valve means to cause said valve means to be conductive during each of a plurality of spaced intervals.

2. Apparatus for use in supplying current to a load comprising a capacitor, charging means connected across said capacitor and tending to supply current therethrough to charge the same Whenever the capacitor voltage is below a predetermined value, circuit means connecting said ca pacitor across said load to eiiect discharge of said capacitor therethrough, said circuit means including valve means interposed between said capacitor and load for controlling the iiow of current therebetween and a resistor in series with said valve means through which passes only the current conducted through said valve means, control means connected to said valve means to cause said valve means to be conductive during each of a plurality of spaced intervals, and means connected to said resistor and to said charging means and responsive to the potential developed across said resistor by a flow of current therethrough to prevent operation of said charging means only during such current flow.

3. Apparatus forv use in supplying current to a load comprising a capacitor, charging means connected across said capacitor and tending to supplycurrent therethrough to charge the same whenever the capacitor potential is -below a predetermined value, circuit means connecting said capacitor across said load to eiiect dischargeof said capacitor therethrough, said circuit means including valve means interposed between said capacitor and load for controlling the iiow of current therebetween and a resistor in series with said valve means through which passes only the current conductedV through said valve means, control means connected to said valve means to cause said valve means to be conductive during each of a plurality of spaced intervals, a transformer having a primary and a secondary Winding with the primary winding connected in circuit across said resistor, said transformer being of the type in which the wave-form of the voltage across the secondary winding is substantially the same as that of the voltage across the primary winding, and means connected to said secondary winding for preventing operation of said charging means only while said valve means is conductive and in response to the voltage developed across said resistor by a flow of current therethrough.

4. Apparatus for use in supplying current to a ll load comprising a capacitor, charging means connected across said capacitor and tending to supply current therethrough to charge the same whenever the capacitor potential is below a predetermined value, circuit means connecting said capacitor across said load to effect discharge of said capacitor therethrough, said circuit means including valve means interposed between said capacitor and load for controlling the flow of current therebetween and a resistor in series with said valve means through which passes only the current conducted through said valve means, control means connected to said valve means to Cause said valve means to be conductive during each of a plurality of spaced intervals, a transformer having a primary and a secondary winding with the primary winding connected in circuit across said resistor, said transformer being of the type in which the wave-form of the voltage across the secondary winding is the same as that of the voltage across the primary winding, said charging means including second control means responsive to the impressing thereon of a direct current voltage of a predetermined polarity and minimum magnitude to prevent operation of said charging means, and means including an ampliiier having an input circuit supplied from said secondary winding for impressing a direct current voltage of at least said predetermined minimum magnitude and of said polarity on said second control means throughout substantially the entire interval of current iiow through said resistor.

5. Apparatus for use in supplying current to an inductive load comprising a capacitor, charging means connected across said capacitor and tending to supply current therethrough to charge the same with a predetermined polarity whenever the capacitor potential is below a preselected value, circuit means connecting said capacitor across said load including a iirst electric discharge valve of the arc-like type interposed between said capa'citor and load for controlling the discharge of 'said capacitor through said load, control means connected to said rst valve to render it conductive at spaced intervals, a second electric discharge valve of the arc-like type connected in parallel circuit relation to said capacitor and iirst valve, and means connected to said second valve and to said load to render said second valve conductive following each discharge of said capacitor to conduct current resulting from a release of the energy stored in said load during the dis-4 charge, said circuit means also including impedance means in series with said rst valve and said parallel connected second valve and load whereby f a voltage is developed across said impedance means by current passing though said rst valve, and means responsive to said voltage and connected to said charging means to prevent operation thereof only while said Voltage is present.

6. Apparatus for use in supplying current to a 12 load through a magnetic core transformer having primary and second windings with said secondary winding being connected in circuit with said load, comprising a capacitor, means connected across said capacitor to supply charging current therethrough whenever the capacitor potential is below a predetermined value, means including normally nonccnductive valve means connecting said capacitor in circuit across said primary winding whereby an oscillating current tends to flow through said primary winding when said valve means is conductive, control means connected to said valve means for rendering the same conductive at spaced intervals to permit a full cycle of oscillating current to flow' through said primary winding, impedance means in series with said valve means whereby a voltage is develope-d across said impedance means by current conducted through said valve means, and means responsive to said voltage and connected to said charging means for preventing operation of said charging means only while valve means is conductive.

'7'. Apparatus for use in supplying current to a load through a magnetic core transformer having primary and secondary windings with said secondary winding being connected in circuit with said load, comprising a capacitor, means connected across said capacitor to supply charging current therethrough whenever the capacitor potential is below a predetermined value, means including normally non-conductive valve means connecting said capacitor in circuit across said primary 'winding' whereby an oscillating current tends to now through said primary winding when 'said valve means is conductive, control means connected to said valve means for rendering the same conductive at spaced intervals to permit a single cycle of oscillating current to flow through -said primary winding, a resistor in series with said valve means, a second transformer having a primary and a secondary winding with the primary winding connected in circuit across said resistor, said second transformer being of the type in which the wave form of the voltage across the secondary winding is the same as that of the prie mary winding voltage, said charging means including Second control means responsive to the impressing thereon of a direct current voltage ci a predetermined minimum magnitude and polarity to prevent operation o'f said charging means, and means including a rectifier connected across the secondary winding of said second transformer and an amplier supplied from said rectifier for impressing a direct current voltage of at least said predetermined minimum magnitude and said polarity on said control means throughout sub stantially all said single cycle of oscillating current.

JOI-IN R. MAHONEY. HARRY J. BICHSEL. 

